Installing asphalt shingles is a bottom-to-top process that starts with preparing the roof deck and ends with capping the ridge. Each layer overlaps the one below it so water flows downhill without finding a way in. The job is straightforward in concept, but the details matter: nail placement off by an inch or a missing layer of underlayment can cut a 30-year roof’s lifespan in half.
Safety Before You Start
Any roof work 6 feet or more above the ground requires fall protection. For steep roofs, that means a personal fall arrest system: a harness anchored to the roof deck. For lower-slope roofs, a guardrail system or safety net can substitute. Hard hats protect against falling objects, and rubber-soled shoes with good grip are essential on shingle surfaces, especially in warm weather when asphalt softens. Set up your ladder on firm, level ground and have a helper available to pass materials up rather than carrying bundles while climbing.
Check Your Roof Slope
Asphalt shingles require a minimum roof slope of 2:12, meaning the roof rises at least 2 inches for every 12 inches of horizontal run. If your slope falls between 2:12 and 4:12, building code requires a double layer of underlayment across the entire deck. Roofs steeper than 4:12 can use a single layer. If your roof is flatter than 2:12, asphalt shingles aren’t appropriate and you’ll need a different roofing material entirely.
Install Underlayment and Drip Edge
Once the deck is clean, dry, and any damaged sheathing is replaced, you’ll install drip edge and underlayment. The layering order matters because it controls where water goes. Along the eaves (the bottom horizontal edge), the drip edge goes on first, directly against the deck. Then the underlayment rolls out on top of it. Along the rakes (the sloped side edges), the order reverses: underlayment goes down first, and the drip edge is nailed over it.
This sequence ensures that water running down the underlayment drops over the drip edge at the eaves, while water blowing sideways at the rakes hits drip edge first and slides under onto the underlayment. In cold climates where ice dams form, use a self-adhering waterproof membrane (often called ice and water shield) along the eaves, extending at least 24 inches past the interior wall line. Roll the rest of the roof with synthetic or felt underlayment, overlapping each course by a few inches as you work upward.
Lay the Starter Course
The starter course is the first row of shingles along the eave, and its job is to back up the joints in the first visible course above it. Without it, water could seep through the gaps between your first-row shingles and reach the deck.
Purpose-made starter strips come with a factory-applied adhesive strip. Position them so the adhesive faces up along the eave edge, which bonds to the bottom of the first course and resists wind uplift. Starter strips should overhang the drip edge by no more than three-quarters of an inch. Too much overhang and the shingle edge will sag or break over time. Too little and water can wick back under the edge. Fasten each strip with five nails placed 2 to 3 inches from the eave edge.
Install the First and Successive Courses
With the starter course in place, your first full course of shingles goes directly on top, aligned with the starter strip’s edge. From here, you’ll work your way up the roof one horizontal row at a time.
The critical detail is the offset. Each row must be staggered horizontally so that the vertical seams between shingles never line up with the seams in the row directly below. The minimum offset is 4 inches between joints on consecutive courses. Most three-tab shingles use a 6-inch offset pattern, where each successive course starts half a tab further along. Architectural (laminated) shingles are more forgiving because of their random appearance, but the 4-inch minimum still applies. Joints that line up, or that are offset by less than 4 inches, create a direct path for water to reach the underlayment and eventually the deck.
Each shingle has a manufacturer-specified nailing zone, typically a narrow band just above the adhesive strip. This zone is where your nails anchor through two overlapping shingle layers at once. Placing nails too high, above this zone, is one of the most common installation failures. High-nailed shingles are held by only one layer of material, leaving the bottom edge free to lift in the wind. The adhesive strip alone can’t compensate for a misplaced nail, especially on steep slopes where gravity pulls the shingle downward. A high-nailed roof can fail in 6 to 10 years instead of the expected 25 to 30, and most manufacturer warranties are voided if nails aren’t in the specified zone.
Use four nails per shingle in standard conditions and six in high-wind zones. Drive each nail flush with the shingle surface. Overdriven nails break through the mat and lose holding power. Underdriven nails sit proud and create a bump that prevents the shingle above from sealing flat.
Handle Valleys Correctly
Valleys, where two roof planes meet, concentrate more water than any other part of the roof. There are two common approaches: open valleys and closed-cut valleys.
An open valley uses a metal flashing liner running down the center, with shingles trimmed back a few inches on each side to leave the metal exposed. This creates a visible channel for water and works especially well with architectural shingles, since their thickness can look bulky when overlapped in a valley. The drawback is cost and the extra fabrication involved. You also need to avoid nailing through the metal, which means relying on roofing cement to hold trimmed shingle edges in place.
A closed-cut valley is faster. Shingles from one roof plane extend across the valley onto the adjacent plane. Then shingles from the second plane are laid on top and cut in a straight line about 2 inches from the valley center. This gives a clean look and keeps the valley covered, but provides only single-layer shingle coverage at the valley center. Regardless of method, waterproof membrane should line every valley beneath the shingles.
When trimming shingles near a valley, clip the upper corner of each cut shingle at a 45-degree angle. This “dubbing” prevents the corner from channeling water sideways under the adjacent shingle.
Work Around Vents and Penetrations
Pipes, vents, and chimneys interrupt the shingle pattern and need flashing to stay watertight. For pipe boots, shingle up to the pipe, then set the boot flange over the pipe so the base sits on top of the shingles below and tucks under the shingles above. The upper portion of the flange should always be covered by the next course of shingles. Apply roofing sealant under the flange edges, but don’t rely on sealant alone.
Near valleys and penetrations, pay extra attention to your offsets. Joints should fall no closer than 4 inches from any flashing edge or valley center line. If your stagger pattern puts a seam too close, adjust the starting point of that course.
Cap the Ridge and Hips
Ridge cap shingles are the finishing layer along the peak where two roof planes meet. You can buy purpose-made ridge cap shingles, which are pre-scored to fold over the ridge and often pre-tapered so edges don’t peek out on either side. Some products are perforated so you can separate them by hand into individual pieces.
On hips (the angled ridges running from peak to eave), start at the bottom and work up, trimming the first piece so its corners don’t hang into the gutter. On the main ridge of a gable roof, start at the end opposite the prevailing wind direction. This way the wind blows over the lapped edges rather than under them, improving wind resistance.
Each ridge cap piece overlaps the one before it by about 5 inches. Nail each piece with two nails, placed about 5 and 5/8 inches above the butt edge and 1 inch in from each side. Use nails at least 2 inches long, since they’re passing through multiple shingle layers plus the ridge board. The final piece gets a dab of roofing cement over the exposed nail heads.
Temperature and Timing
Asphalt shingles have a built-in adhesive strip that bonds each shingle to the one above it. This strip needs heat to activate, reaching about 70°F at the shingle surface. The ideal air temperature for installation is between 45°F and 85°F. Within that range, sun exposure warms the shingles enough to trigger a strong seal. Most manufacturers recommend at least two consecutive days above 40°F after installation for proper bonding.
Installing in cold weather isn’t impossible, but the shingles won’t seal immediately. They’ll remain vulnerable to wind until warmer temperatures arrive. Cold shingles are also more brittle and prone to cracking when bent or nailed. On the other end, working in extreme heat makes shingles soft and easy to scuff with foot traffic, and the roofing surface itself becomes a serious heat exposure risk.
If you’re installing in cooler conditions, handle shingles carefully and store bundles in a warm area before bringing them to the roof. In hot weather, work early in the morning and avoid dragging tools or feet across freshly laid shingles.